1. What are delegates?
2. What we can do with the delegates?
The CLR allows defining delegates which is a type-safety way of using callback methods. Delegate indicates the signatures of a callback method.
We can combine delegates into their chains and work with this chain. For example we can add and remove delegates from the chains. The C# also provides working with delegates with easy-to-use syntax.
Example:
class Program
{
//Delegate indicates the signatures of a callback method
internal delegate void Feedback(int value);
static void Main(string[] args)
{
StaticCalling();
InstanceCalling();
ChainCallingDemo1(new Program());
ChainCallingDemo2(new Program());
Console.ReadKey();
}
private static void StaticCalling()
{
CallNTimes(5, new Feedback(StaticMethod));
}
private static void InstanceCalling()
{
CallNTimes(3, new Feedback(new Program().InstanceMethod));
}
private static void ChainCallingDemo1(Program p)
{
Feedback fb1 = new Feedback(StaticMethod);
Feedback fb2 = new Feedback(p.InstanceMethod);
//We can combine delegtes into their chains
Feedback fbChain = null;
fbChain = (Feedback)Delegate.Combine(fbChain, fb1);
fbChain = (Feedback)Delegate.Combine(fbChain, fb2);
Console.WriteLine("Chain calling after the Delegate.Combine");
CallNTimes(1, fbChain);
//We can remove delegates from their chains
Console.WriteLine("Chain calling after the Delegate.Remove");
fbChain = (Feedback)Delegate.Remove(fbChain, fb1);
CallNTimes(1, fbChain);
}
private static void ChainCallingDemo2(Program p)
{
Feedback fb1 = new Feedback(StaticMethod);
Feedback fb2 = new Feedback(p.InstanceMethod);
//We can combine delegates into their chains with easy-to-use syntax
Feedback fbChain = null;
fbChain += fb1;
fbChain += fb2;
Console.WriteLine("Chain calling after the Delegate.Combine");
CallNTimes(1, fbChain);
//We can remove delegtes from their chains with easy-to-use syntax
Console.WriteLine("Chain calling after the Delegate.Remove");
fbChain -= fb1;
CallNTimes(1, fbChain);
}
private static void CallNTimes(int n, Feedback fb)
{
//before delegate calling we must check its existance
if (fb != null)
{
int i = 0;
while (i < n)
{
fb(i++);
}
}
}
private static void StaticMethod(int value)
{
Console.WriteLine("The StaticMethod was called: {0}", value);
}
private void InstanceMethod(int value)
{
Console.WriteLine("The InstanceMethod was called: {0}", value);
}
}
Grigory's space 